From b65a9d33cd1241326d2659d7a39f155127e382f5 Mon Sep 17 00:00:00 2001
From: Siddharth Ganesan <siddharthganesan@gmail.com>
Date: Fri, 9 Jan 2026 17:18:16 -0800
Subject: [PATCH 1/5] Fix router block

---
 .../condition-input/condition-input.tsx       | 15 +++++++---
 .../workflow-block/workflow-block.tsx         |  6 ++--
 apps/sim/blocks/blocks/router.ts              | 28 +++++++++++--------
 .../handlers/router/router-handler.ts         |  9 +++---
 bun.lock                                      |  1 -
 5 files changed, 36 insertions(+), 23 deletions(-)

diff --git a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/editor/components/sub-block/components/condition-input/condition-input.tsx b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/editor/components/sub-block/components/condition-input/condition-input.tsx
index 9801a4f57e..70f8691092 100644
--- a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/editor/components/sub-block/components/condition-input/condition-input.tsx
+++ b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/editor/components/sub-block/components/condition-input/condition-input.tsx
@@ -654,16 +654,19 @@ export function ConditionInput({
   }
 
   const removeBlock = (id: string) => {
-    if (isPreview || disabled || conditionalBlocks.length <= 2) return
+    if (isPreview || disabled) return
+    // Condition mode requires at least 2 blocks (if/else), router mode requires at least 1
+    const minBlocks = isRouterMode ? 1 : 2
+    if (conditionalBlocks.length <= minBlocks) return
 
     // Remove any associated edges before removing the block
+    const handlePrefix = isRouterMode ? `router-${id}` : `condition-${id}`
     edges.forEach((edge) => {
-      if (edge.sourceHandle?.startsWith(`condition-${id}`)) {
+      if (edge.sourceHandle?.startsWith(handlePrefix)) {
         removeEdge(edge.id)
       }
     })
 
-    if (conditionalBlocks.length === 1) return
     shouldPersistRef.current = true
     setConditionalBlocks((blocks) => updateBlockTitles(blocks.filter((block) => block.id !== id)))
 
@@ -815,7 +818,11 @@ export function ConditionInput({
                   <Button
                     variant='ghost'
                     onClick={() => removeBlock(block.id)}
-                    disabled={isPreview || disabled || conditionalBlocks.length === 1}
+                    disabled={
+                      isPreview ||
+                      disabled ||
+                      conditionalBlocks.length <= (isRouterMode ? 1 : 2)
+                    }
                     className='h-auto p-0 text-[var(--text-error)] hover:text-[var(--text-error)]'
                   >
                     <Trash className='h-[14px] w-[14px]' />
diff --git a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/workflow-block/workflow-block.tsx b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/workflow-block/workflow-block.tsx
index efa8ddb2d9..7cd7863913 100644
--- a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/workflow-block/workflow-block.tsx
+++ b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/workflow-block/workflow-block.tsx
@@ -863,7 +863,8 @@ export const WorkflowBlock = memo(function WorkflowBlock({
           return parsed.map((item: unknown, index: number) => {
             const routeItem = item as { id?: string; value?: string }
             return {
-              id: routeItem?.id ?? `${id}-route-${index}`,
+              // Use stable ID format that matches ConditionInput's generateStableId
+              id: routeItem?.id ?? `${id}-route${index + 1}`,
               value: routeItem?.value ?? '',
             }
           })
@@ -873,7 +874,8 @@ export const WorkflowBlock = memo(function WorkflowBlock({
       logger.warn('Failed to parse router routes value', { error, blockId: id })
     }
 
-    return [{ id: `${id}-route-route1`, value: '' }]
+    // Fallback must match ConditionInput's default: generateStableId(blockId, 'route1') = `${blockId}-route1`
+    return [{ id: `${id}-route1`, value: '' }]
   }, [type, subBlockState, id])
 
   /**
diff --git a/apps/sim/blocks/blocks/router.ts b/apps/sim/blocks/blocks/router.ts
index ae6672a309..a67cff0fde 100644
--- a/apps/sim/blocks/blocks/router.ts
+++ b/apps/sim/blocks/blocks/router.ts
@@ -115,25 +115,29 @@ Description: ${route.value || 'No description provided'}
     )
     .join('\n')
 
-  return `You are an intelligent routing agent. Your task is to analyze the provided context and select the most appropriate route from the available options.
+  return `You are a DETERMINISTIC routing agent. You MUST select exactly ONE route. There is NO other option.
+
+CRITICAL RULES:
+- You MUST output a route ID. Period.
+- You CANNOT say "I need more information"
+- You CANNOT refuse to choose
+- You CANNOT explain your reasoning
+- You CANNOT ask questions
+- You CANNOT output anything except a route ID
+- There is ALWAYS a best option. Pick it.
 
 Available Routes:
 ${routesInfo}
 
-Context to analyze:
+Context:
 ${context}
 
-Instructions:
-1. Carefully analyze the context against each route's description
-2. Select the route that best matches the context's intent and requirements
-3. Consider the semantic meaning, not just keyword matching
-4. If multiple routes could match, choose the most specific one
-
-Response Format:
-Return ONLY the route ID as a single string, no punctuation, no explanation.
-Example: "route-abc123"
+MANDATORY BEHAVIOR:
+1. Analyze the context against each route description
+2. ALWAYS pick the BEST matching route - one route is always better than the others
+3. Output ONLY the route ID - nothing else
 
-Remember: Your response must be ONLY the route ID - no additional text, formatting, or explanation.`
+Your response must be EXACTLY one route ID from the list above. No punctuation. No explanation. No refusal. Just the ID.`
 }
 
 /**
diff --git a/apps/sim/executor/handlers/router/router-handler.ts b/apps/sim/executor/handlers/router/router-handler.ts
index d702a1b80f..6047e32d52 100644
--- a/apps/sim/executor/handlers/router/router-handler.ts
+++ b/apps/sim/executor/handlers/router/router-handler.ts
@@ -273,14 +273,15 @@ export class RouterBlockHandler implements BlockHandler {
       const result = await response.json()
 
       const chosenRouteId = result.content.trim()
-      const chosenRoute = routes.find((r) => r.id === chosenRouteId)
+      let chosenRoute = routes.find((r) => r.id === chosenRouteId)
 
+      // Fallback to first route if LLM returns invalid route ID
       if (!chosenRoute) {
-        logger.error(
-          `Invalid routing decision. Response content: "${result.content}", available routes:`,
+        logger.warn(
+          `Invalid routing decision. Response content: "${result.content}", falling back to first route. Available routes:`,
           routes.map((r) => ({ id: r.id, title: r.title }))
         )
-        throw new Error(`Invalid routing decision: ${chosenRouteId}`)
+        chosenRoute = routes[0]
       }
 
       // Find the target block connected to this route's handle
diff --git a/bun.lock b/bun.lock
index c08c899810..ad4825181d 100644
--- a/bun.lock
+++ b/bun.lock
@@ -1,6 +1,5 @@
 {
   "lockfileVersion": 1,
-  "configVersion": 0,
   "workspaces": {
     "": {
       "name": "simstudio",

From 9d7ab37e3d6338e1513faee8c6cb9cb6117ed44a Mon Sep 17 00:00:00 2001
From: Siddharth Ganesan <siddharthganesan@gmail.com>
Date: Fri, 9 Jan 2026 17:21:19 -0800
Subject: [PATCH 2/5] Fix autoconnect edge for router

---
 .../workspace/[workspaceId]/w/[workflowId]/workflow.tsx   | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/workflow.tsx b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/workflow.tsx
index 876ee009a4..480571f063 100644
--- a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/workflow.tsx
+++ b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/workflow.tsx
@@ -969,6 +969,14 @@ const WorkflowContent = React.memo(() => {
         const handleId = conditionHandles[0].getAttribute('data-handleid')
         if (handleId) return handleId
       }
+    } else if (block.type === 'router_v2') {
+      const routerHandles = document.querySelectorAll(
+        `[data-nodeid^="${block.id}"][data-handleid^="router-"]`
+      )
+      if (routerHandles.length > 0) {
+        const handleId = routerHandles[0].getAttribute('data-handleid')
+        if (handleId) return handleId
+      }
     } else if (block.type === 'loop') {
       return 'loop-end-source'
     } else if (block.type === 'parallel') {

From d7718e6b84bb1634c8fb9990ae93e2aee5453cad Mon Sep 17 00:00:00 2001
From: Siddharth Ganesan <siddharthganesan@gmail.com>
Date: Fri, 9 Jan 2026 17:21:27 -0800
Subject: [PATCH 3/5] Fix lint

---
 .../sub-block/components/condition-input/condition-input.tsx  | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/editor/components/sub-block/components/condition-input/condition-input.tsx b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/editor/components/sub-block/components/condition-input/condition-input.tsx
index 70f8691092..387d8e2f1f 100644
--- a/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/editor/components/sub-block/components/condition-input/condition-input.tsx
+++ b/apps/sim/app/workspace/[workspaceId]/w/[workflowId]/components/panel/components/editor/components/sub-block/components/condition-input/condition-input.tsx
@@ -819,9 +819,7 @@ export function ConditionInput({
                     variant='ghost'
                     onClick={() => removeBlock(block.id)}
                     disabled={
-                      isPreview ||
-                      disabled ||
-                      conditionalBlocks.length <= (isRouterMode ? 1 : 2)
+                      isPreview || disabled || conditionalBlocks.length <= (isRouterMode ? 1 : 2)
                     }
                     className='h-auto p-0 text-[var(--text-error)] hover:text-[var(--text-error)]'
                   >

From f1b8745625ee1db81d5d1fbcf967a9ba08781ba4 Mon Sep 17 00:00:00 2001
From: Vikhyath Mondreti <vikhyath@simstudio.ai>
Date: Sat, 10 Jan 2026 10:59:35 -0800
Subject: [PATCH 4/5] router block error path decision

---
 apps/docs/content/docs/en/blocks/router.mdx   | 10 +++++++--
 apps/sim/blocks/blocks/router.ts              | 18 +++++++++-------
 .../handlers/router/router-handler.ts         | 21 +++++++++++++------
 3 files changed, 33 insertions(+), 16 deletions(-)

diff --git a/apps/docs/content/docs/en/blocks/router.mdx b/apps/docs/content/docs/en/blocks/router.mdx
index e0f916fc83..33c809c3d0 100644
--- a/apps/docs/content/docs/en/blocks/router.mdx
+++ b/apps/docs/content/docs/en/blocks/router.mdx
@@ -2,7 +2,6 @@
 title: Router
 ---
 
-import { Callout } from 'fumadocs-ui/components/callout'
 import { Tab, Tabs } from 'fumadocs-ui/components/tabs'
 import { Image } from '@/components/ui/image'
 
@@ -90,11 +89,18 @@ Input (Lead) → Router → Agent (Enterprise Sales) or Workflow (Self-serve)
 ```
 
 
+## Error Handling
+
+When the Router cannot determine an appropriate route for the given context, it will route to the **error path** instead of arbitrarily selecting a route. This happens when:
+
+- The context doesn't clearly match any of the defined route descriptions
+- The AI determines that none of the available routes are appropriate
+
 ## Best Practices
 
 - **Provide clear target descriptions**: Help the Router understand when to select each destination with specific, detailed descriptions
 - **Use specific routing criteria**: Define clear conditions and examples for each path to improve accuracy
-- **Implement fallback paths**: Connect a default destination for when no specific path is appropriate
+- **Connect an error path**: Handle cases where no route matches by connecting an error handler for graceful fallback behavior
 - **Test with diverse inputs**: Ensure the Router handles various input types, edge cases, and unexpected content
 - **Monitor routing performance**: Review routing decisions regularly and refine criteria based on actual usage patterns
 - **Choose appropriate models**: Use models with strong reasoning capabilities for complex routing decisions
diff --git a/apps/sim/blocks/blocks/router.ts b/apps/sim/blocks/blocks/router.ts
index a67cff0fde..0a3e3a3667 100644
--- a/apps/sim/blocks/blocks/router.ts
+++ b/apps/sim/blocks/blocks/router.ts
@@ -115,29 +115,31 @@ Description: ${route.value || 'No description provided'}
     )
     .join('\n')
 
-  return `You are a DETERMINISTIC routing agent. You MUST select exactly ONE route. There is NO other option.
+  return `You are a DETERMINISTIC routing agent. You MUST select exactly ONE option.
 
 CRITICAL RULES:
-- You MUST output a route ID. Period.
+- You MUST output ONLY a route ID or "NO_MATCH" - copy it EXACTLY as shown
 - You CANNOT say "I need more information"
-- You CANNOT refuse to choose
 - You CANNOT explain your reasoning
 - You CANNOT ask questions
-- You CANNOT output anything except a route ID
-- There is ALWAYS a best option. Pick it.
+- You CANNOT output anything except the exact route ID or "NO_MATCH"
 
 Available Routes:
 ${routesInfo}
 
+Special Option:
+- If the context does NOT clearly match ANY route description, output exactly: NO_MATCH
+
 Context:
 ${context}
 
 MANDATORY BEHAVIOR:
 1. Analyze the context against each route description
-2. ALWAYS pick the BEST matching route - one route is always better than the others
-3. Output ONLY the route ID - nothing else
+2. If one route clearly matches the context, output that route's ID exactly as shown
+3. If NO route is appropriate for the context, output exactly: NO_MATCH
+4. Output ONLY the route ID or NO_MATCH - nothing else
 
-Your response must be EXACTLY one route ID from the list above. No punctuation. No explanation. No refusal. Just the ID.`
+Your response must be EXACTLY one route ID from the list above OR "NO_MATCH". No punctuation. No explanation. Just the ID or NO_MATCH.`
 }
 
 /**
diff --git a/apps/sim/executor/handlers/router/router-handler.ts b/apps/sim/executor/handlers/router/router-handler.ts
index 6047e32d52..63e327f390 100644
--- a/apps/sim/executor/handlers/router/router-handler.ts
+++ b/apps/sim/executor/handlers/router/router-handler.ts
@@ -273,15 +273,24 @@ export class RouterBlockHandler implements BlockHandler {
       const result = await response.json()
 
       const chosenRouteId = result.content.trim()
-      let chosenRoute = routes.find((r) => r.id === chosenRouteId)
 
-      // Fallback to first route if LLM returns invalid route ID
+      if (chosenRouteId === 'NO_MATCH' || chosenRouteId.toUpperCase() === 'NO_MATCH') {
+        logger.info('Router determined no route matches the context, routing to error path')
+        throw new Error('Router could not determine a matching route for the given context')
+      }
+
+      const chosenRoute = routes.find((r) => r.id === chosenRouteId)
+
+      // Throw error if LLM returns invalid route ID - this routes through error path
       if (!chosenRoute) {
-        logger.warn(
-          `Invalid routing decision. Response content: "${result.content}", falling back to first route. Available routes:`,
-          routes.map((r) => ({ id: r.id, title: r.title }))
+        const availableRoutes = routes.map((r) => ({ id: r.id, title: r.title }))
+        logger.error(
+          `Invalid routing decision. Response content: "${result.content}". Available routes:`,
+          availableRoutes
+        )
+        throw new Error(
+          `Router could not determine a valid route. LLM response: "${result.content}". Available route IDs: ${routes.map((r) => r.id).join(', ')}`
         )
-        chosenRoute = routes[0]
       }
 
       // Find the target block connected to this route's handle

From f2283d37e52b8de7f288ee69a1adaccbc21362e3 Mon Sep 17 00:00:00 2001
From: Vikhyath Mondreti <vikhyath@simstudio.ai>
Date: Sat, 10 Jan 2026 11:10:02 -0800
Subject: [PATCH 5/5] improve router prompt

---
 apps/sim/blocks/blocks/router.ts | 29 ++++++++++++-----------------
 1 file changed, 12 insertions(+), 17 deletions(-)

diff --git a/apps/sim/blocks/blocks/router.ts b/apps/sim/blocks/blocks/router.ts
index 4339addfa5..ecc48f5b70 100644
--- a/apps/sim/blocks/blocks/router.ts
+++ b/apps/sim/blocks/blocks/router.ts
@@ -117,29 +117,24 @@ Description: ${route.value || 'No description provided'}
 
   return `You are a DETERMINISTIC routing agent. You MUST select exactly ONE option.
 
-CRITICAL RULES:
-- You MUST output ONLY a route ID or "NO_MATCH" - copy it EXACTLY as shown
-- You CANNOT say "I need more information"
-- You CANNOT explain your reasoning
-- You CANNOT ask questions
-- You CANNOT output anything except the exact route ID or "NO_MATCH"
-
 Available Routes:
 ${routesInfo}
 
-Special Option:
-- If the context does NOT clearly match ANY route description, output exactly: NO_MATCH
-
-Context:
+Context to route:
 ${context}
 
-MANDATORY BEHAVIOR:
-1. Analyze the context against each route description
-2. If one route clearly matches the context, output that route's ID exactly as shown
-3. If NO route is appropriate for the context, output exactly: NO_MATCH
-4. Output ONLY the route ID or NO_MATCH - nothing else
+ROUTING RULES:
+1. ALWAYS prefer selecting a route over NO_MATCH
+2. Pick the route whose description BEST matches the context, even if it's not a perfect match
+3. If the context is even partially related to a route's description, select that route
+4. ONLY output NO_MATCH if the context is completely unrelated to ALL route descriptions
+
+OUTPUT FORMAT:
+- Output EXACTLY one route ID (copied exactly as shown above) OR "NO_MATCH"
+- No explanation, no punctuation, no additional text
+- Just the route ID or NO_MATCH
 
-Your response must be EXACTLY one route ID from the list above OR "NO_MATCH". No punctuation. No explanation. Just the ID or NO_MATCH.`
+Your response:`
 }
 
 /**